XArray: Add xa_cmpxchg_irq and xa_cmpxchg_bh

These convenience wrappers match the other _irq and _bh wrappers we
already have.  It turns out I'd already open-coded xa_cmpxchg_irq()
in the shmem code, so convert that.
Signed-off-by: Matthew Wilcox <willy@infradead.org>

Documentation/core-api/xarray.rst

@@ -187,6 +187,8 @@ Takes xa_lock internally:
  * :c:func:`xa_erase_bh`
  * :c:func:`xa_erase_irq`
  * :c:func:`xa_cmpxchg`
+ * :c:func:`xa_cmpxchg_bh`
+ * :c:func:`xa_cmpxchg_irq`
  * :c:func:`xa_store_range`
  * :c:func:`xa_alloc`
  * :c:func:`xa_alloc_bh`
@@ -263,7 +265,8 @@ using :c:func:`xa_lock_irqsave` in both the interrupt handler and process
 context, or :c:func:`xa_lock_irq` in process context and :c:func:`xa_lock`
 in the interrupt handler.  Some of the more common patterns have helper
 functions such as :c:func:`xa_store_bh`, :c:func:`xa_store_irq`,
-:c:func:`xa_erase_bh` and :c:func:`xa_erase_irq`.
+:c:func:`xa_erase_bh`, :c:func:`xa_erase_irq`, :c:func:`xa_cmpxchg_bh`
+and :c:func:`xa_cmpxchg_irq`.
 
 Sometimes you need to protect access to the XArray with a mutex because
 that lock sits above another mutex in the locking hierarchy.  That does

include/linux/xarray.h

@@ -553,6 +553,60 @@ static inline void *xa_cmpxchg(struct xarray *xa, unsigned long index,
 	return curr;
 }
 
+/**
+ * xa_cmpxchg_bh() - Conditionally replace an entry in the XArray.
+ * @xa: XArray.
+ * @index: Index into array.
+ * @old: Old value to test against.
+ * @entry: New value to place in array.
+ * @gfp: Memory allocation flags.
+ *
+ * This function is like calling xa_cmpxchg() except it disables softirqs
+ * while holding the array lock.
+ *
+ * Context: Any context.  Takes and releases the xa_lock while
+ * disabling softirqs.  May sleep if the @gfp flags permit.
+ * Return: The old value at this index or xa_err() if an error happened.
+ */
+static inline void *xa_cmpxchg_bh(struct xarray *xa, unsigned long index,
+			void *old, void *entry, gfp_t gfp)
+{
+	void *curr;
+
+	xa_lock_bh(xa);
+	curr = __xa_cmpxchg(xa, index, old, entry, gfp);
+	xa_unlock_bh(xa);
+
+	return curr;
+}
+
+/**
+ * xa_cmpxchg_irq() - Conditionally replace an entry in the XArray.
+ * @xa: XArray.
+ * @index: Index into array.
+ * @old: Old value to test against.
+ * @entry: New value to place in array.
+ * @gfp: Memory allocation flags.
+ *
+ * This function is like calling xa_cmpxchg() except it disables interrupts
+ * while holding the array lock.
+ *
+ * Context: Process context.  Takes and releases the xa_lock while
+ * disabling interrupts.  May sleep if the @gfp flags permit.
+ * Return: The old value at this index or xa_err() if an error happened.
+ */
+static inline void *xa_cmpxchg_irq(struct xarray *xa, unsigned long index,
+			void *old, void *entry, gfp_t gfp)
+{
+	void *curr;
+
+	xa_lock_irq(xa);
+	curr = __xa_cmpxchg(xa, index, old, entry, gfp);
+	xa_unlock_irq(xa);
+
+	return curr;
+}
+
 /**
  * xa_insert() - Store this entry in the XArray unless another entry is
  *			already present.

mm/shmem.c

@@ -661,9 +661,7 @@ static int shmem_free_swap(struct address_space *mapping,
 {
 	void *old;
 
-	xa_lock_irq(&mapping->i_pages);
-	old = __xa_cmpxchg(&mapping->i_pages, index, radswap, NULL, 0);
-	xa_unlock_irq(&mapping->i_pages);
+	old = xa_cmpxchg_irq(&mapping->i_pages, index, radswap, NULL, 0);
 	if (old != radswap)
 		return -ENOENT;
 	free_swap_and_cache(radix_to_swp_entry(radswap));